Electromagnetic rectifier



Sept 22, 1959 E. J. DIEBOLD 2,905,884

ELECTROMAGNETIC RECTIFIER Filed Dec. 12, 1955 '1 sheets-sheet 1 sept.22, 1959 Filed Dec. l2, 1955 E. J. DIEBOLD ELECTROMAGNETIC RECTIFIER 7Sheets-Sheet 2 BY WM/W Sept. 22, 1959 E. J. DIEBOLD ELECTROMAGNETICkRECTIFIEIR 7 Sheets-Sheet 3 Filed Dec. 12, 1955 Sept. 22, 1959 FiledDec. l2, 1955 E. J. Dlt-:BOLD 2,905,884

ELECTROMAGNETIC RECTIFIER '7 Sheets-Sheet 4 Sept. 22, 1959 Filed Dec.12, 1955 E. J. DIEBOLD ELECTROMAGNETIC RECTIFIER 7 Sheets-Sheet 5 Sept.22, 1959 Filed Dec. 12, 1955 E. J. DIEBOLD ELECTROMAGNETIC RECTIFIER 7Sheets-Sheet 6 Sept. 22, 1959 E. J. DIEBOLD ELECTROMAGNETIC RECTIFIER '7Sheets-Sheet 7 Filed Dec. 12, 1.955

.mmikwhmlmmll United States Patent O ELECTROMAGNETIC RECTIFIER .EdwardJohn Diebold, Ardmore, Pa., assigner to I-T-E Circuit Breaker Company,Philadelphia, Pa., a corporation of Pennsylvania Application December12, 1955, Serial No. 552,562

17 Claims. (Cl. 321-48) My invention relates to `a new circuitry forelectromagnetic rectifiers and more specifically 'to a new circuitrywhich is based on the understanding of inherent problems which have notbeen understood heretofore.

The basic theory of an electromagnetic rectifier is as follows: Aferromagnetic and electrically conductive body of small size is moved byelectromagnetic forces between magnet poles which also serve as fixedelectrical conductors. Magnetization of the poles attracts the movablebody to establish an electrical circuit when the movable body engagesthe magnet poles.

Demagnetization of the poles then releases Vthe movable Abody `which issubsequently carried away by a biasing means which can `be va spring oranother magnetic field. Electric current which liows through the circuitestablished by the movable ybody is used to produce the magnetic fieldholding it against the 'poles and loss of this current will cause therelease of the body.

A small auxiliary current which does not iiow through the circuitestablished by the movable body is used to build up the magnetic fieldrequired to close Vthis circuit. Control of the time at which the smallauxiliary current rises affords control of the large current yflowinginthe circuit established by the movable body.

Electromagnetic rectifiers operating Yaccording to the above statedprinciples have been described in my 'U.S. -Pa-tent No. 2,756,380,issued July 24, 1956 entitled Electromagnetic Switch, to E. J. Dieboldand assigned tothe assignee of the present invention. Theelectromagnetic switch which supplies the above-mentioned magneticpolesyand current carrying armature to which Vthe circuitry describedhereinafter can be applied, is -shown in U;S. Patent No. 2,805,300,issued September 13, 1957 entitled Electromagnetic Contact Device, to E.J. VDiebold and VElmer Goessel and assigned to -the Vassignee vof lthepresent invention.

-Severe problems have confronted the development of theelectromagneticrectifier iin the -past such as the rrectitiershown-intheaboveementionedUS. kPatent-No. 2,7 5 6,- 380 because of a mistaken assumption as to theoperationof the mechanical switch. That is, in the past, it `was`implicitly assumed that `the mechanical requirements forelectromagnetically operated contacts zare Zsimple and rthat they aresatisfied lto va -degree that their existence couldfbe ignored lby thepractical contacts. fHence, no effort was made to compensate for the:mechanicalshortcornings iby anadequate design of the electricalcircuitry. ein fact, conditions governing Jthe design of the electricalcommutation circuits werebased on'the rules established with mechanical'rectifiers such Aas .the rectifier shown in U;S. Patent No. 2,759,141,issued August 14, 1956 entitled Regulator for Mechanical Rectifier, .-toE. J.

Diebold and assigned to '.the `assignee `of the ,present inr erated-mechanically instead of byaelectromagneticfields.

Braetical experience, however, `shows that :these ;as

nice,

sumptions are not justified but have to be replaced by new concept of anelectromagnetic rectifier.

Conditions derived from past experience express ythe problems which mustbe solved by the electrical circuit operating in conjunction with theContact and these con `ditions are as follows: i

(l) Glow discharge between approaching or separating contacts'will startwhenever the most favorable dis'- tance is reached, i.e., when the gapseparating the contact surfaces is equivalent to approximately the meanfree path of the gas vmolecules between them. The sm'aliest voltagecausing a glow-discharge in the air is approximately 280 volts and thefavorable distance for Aatmosppheric fair is 0.000300". Increasing thepressure will decrease the rfavorable distance, but will not increaseAthe smallest voltage as by `the Law o-f Paschen. Contacts `should notapproach the critical distance ata voltage equal or higher than theminimum glow-discharge voltage, because the glow-discharge will cause anare which is destructive for the contact material.

(2) Capacitive energy is stored between adjacent contacts, theconductors and other components connected to them, and will be liberatedinstantaneously at the make vof the contacts. lf `this energy is inexcess of two ergs (200 billionths of a watt second), it will be a causeof `transfer of matter which will destroy the contacts after a certainnumber of operations. This is particularly dangerous ifAsp-ark-extinguishing capacitors are connected across the contact. It isalso dangerous for normal contaets due to the increase of capacity whilecontacts are approaching if the yvoltage charging this increasingcapacitance is too high. In the practical case, if voltage `acrossclosing contact at the closing `instant is lower than ten volts, thefield discharge of electrons which is .the cause of damage will notoccur and therefore 4no transfer of matter is experienced. At highervoltages field discharge occurs when the contacts yhave approached adistance varying between l0 to 100 microinches due to the excessivelylhigh voltage gradient existing vbetween ythem.

Volume of matter transferred due to held-discharge which leads toultimate contact destruction, is proporitional to the Vdischargecapacity and the square of the Vbreak-down voltage.

(3) The discharge time-,constant of the distributed capacitances andeventually used spark-extinguisher-par- -allel path, determines the timeduing which voltage must be kept at the minimum voltage specified `undercondition v2.

(4) Velocity between contacts during the make process should be at leasttwenty inches per second. A lower velocity means a longer transitionVtime during which 4the contact resistance is finite and more heat willbe developed in the co-ntact surface.

(5) Make inrush current should be less than 0.32ampere, the limit for notransfer of matter during contact separation or break. That vis toprotect the contact in case of bounce.

(6) Rate of rise vof contact current, immediatelyafter make, should beless than'ten amperes per Second. This will limit the amount of currentinterrupted in case of contact bounce.

(7) Make `step length 'or the time during which condition l6 must besatisfied, should be longer than eighty microseconds to cover allpossible bouncing.

(8) Current through the contact immediately before and during the breakAshould be less than 0L2 ampere. Break-current will cause contactmaterial to melt. 'The molten bridge formed has an unequal temperaturedistribution due to Thompson-Peltier effect and this results in transferof matter. The amount of matter transferred becomes ynegli-gible if ytheabove condition Ais satisfied since the volume of matter transferred isproportional to the cube of the residual current. This condition,however, as stated, limits the transfer to an amount too small to damagethe contact after approximately one billion operations.

(9) Break current should be opposite in direction to eventuallyoccurring back-fire current. In case of an ,incorrect break an arc willbe drawn which will eventually extinguish when the current in the arcreverses. Not satisfying this condition results in a back-fire wheneveran unusual break operation occurs (start, stop, variation of primaryvoltage, short-circuit of load, etc.).

(l) Energy stored in the magnetic fields around the main conductors,should be dissipated before the actual break occurs. In the practicalcase, a time interval of 20 microseconds before the break during whichthe current is kept at a low value will satisfy this condition.

(11) Velocity of separation of the contacts at the break should be atleast twenty inches per second. This assures steady operation withoutreclosing bounce and limits the amount of material transferred by theresidual current owing through the contact during the break.

(12) Recovery voltage appearing instantaneously at the break should beless than twelve volts, which is the minimum voltage required tomaintain an arc between the practically used contact materials such assilver, gold, platinum, palladium, nickel, tungsten and others or alloysthereof.

(13) Rate of rise of the recovery voltage between the contact surfacesshould be less than 100,000 volts per second. This is to prevent arestrike of an arc during the separation of the contacts.

(14) Deionization time during which the above condition must besatisfied should be approximately 100 to 200 microseconds. This actuallydepends on the amount of ionization available at the break, andtherefore on the way the other conditions are satisfied.

Of the above conditions, numbers 2, 3, and ll are completely new andexpress a method of approach which was, up to now, not followed.Condition 4 is radically changed as it was inadequately expressedbefore. Most of these increased restrictions are due to the presence ofcontact bounce which cannot be eliminated with any degree vof certaintyand therefore is always assumed to be present, even if its occurrence isonly sporadic.

In addition to the conditions expressed above which are specific to thecontacts themselves, another set of conditions have been establishedpertaining to the rectier circuitry in general. Although they are notphysically rigorous, practical experience has proved them to benecessary.

(l5) A circuit operating in conjunction with electromagneticallyoperated contacts should be self-governing and self-controlling toassure correct operation instantaneously and under all circumstances.

(16) There should be compensation for additional voltage drop ofparallel circuits and drive-magnet, assuring a higher output voltage forthe same circuit elements and a higher power factor for the input power.

(17) Operation of rectifier should cease in a sharp cut-off when loadcurrent is less than the limit required by the magneto-motive force ofthe drive magnet. A parallel circuit should carry the current below thislimit.

(18) Make and break operations should be, as much as possible,identical, except occurring in inverse sequence. This will permit use ofthe same elements twice during each cycle and automatically correctoperation in case of a faulty or insuflicient previous operation.

(19) Operation in case of back fire should be sufficiently safe toprevent gross damage and keep equipment in workable condition untilprotective equipment trips.

A review of the above mentioned conditions will emphasize the importanceof low voltage across the contacts during the time the contacts engage.

I now propose the use of a novel circuit which will assure a low makevoltage under all conditions. This novel make pre-excitation circuitwill in fact now become a basic component of any electromagneticrectifier in much the same manner as the electromagnetic switch,commutating reactor and by-pass circuit are basic components.

The principle of this novel invention is to provide a makepre-excitation circuit which will work in conjunction with aconventional by-pass circuit and comprise an electrical valve or diodewhich is connected in parallel with the electro-magnetic switch contactsand in series with the commutating reactor. In the case ofelectromagnetic rectifiers employing voltage control by delaying theinitiation of by-pass circuit current, my novel make pre-excita tioncircuit will be connected in series with the regulating means and theseries connection of the make pre-excitation circuit and regulatingmeans will then be connected across the electromagnetic switch contacts.

The operation of this combination will then allow the conventional typeof by-pass circuit to energize the contact closing while my novel makepre-excitation circuit will be so connected as to drain current throughthe commutating reactor to thereby have the commutating reactorunsaturated or in its step at the time the by-pass circuit closes thecontacts. Therefore, at the time contact engagement occurs, the voltageacross the contact will be the forward voltage drop due to the low stepcurrent of the commutating reactor across the parallel connected diodewhich comprises my novel make pre-excitation circuit and which is ofonly a negligible amount. Furthermore, the commutating reactor will beunsaturated and in its step at the closing time and can therefore be sobiased that the step current which is the inrush current to the contactis either zero or a very small amount.

It should be noted that in the prior art devices, the closing of thecontact initiated the unsaturation of the commutating reactor. Hence,contact inrush current was inherent since the commutating reactor wentfrom a static condition to a dynamic condition. It is well known in theart that there is no practical method of compensating for this inherentinrush current.

However, the use of my novel make pre-excitation circuit places thecommutating reactor in its dynamic condition before contact engagementand therefore allows the use of compensation circuits or biasingcircuits to make the contact inrush current either zero or a very smallvalue.

Accordingly, a primary object of my invention is to provide circuitryfor an electromagnetic switch which will maintain the voltage across theswitch contacts at a low or Zero value during the time the contactsengage and disengage.

Another object of my invention is to provide a make pre-excitationcircuit which will be connected across the contacts of anelectromagnetic switch and comprises a diode which could be in serieswith a regulating means and acts to unsaturate the commutating reactorbefore the electromagnetic switch contacts engage.

Still another object of my invention is to provide a make pre-excitationcircuit for electromagnetic rectiers which comprises a diode connectedacross the electromagnetic switch contacts such that the voltage acrossthe electromagnetic switch contacts when they engage is only the forwardvoltage drop of the diode.

A further object of my invention is to provide a make pre-excitationcircuit which will place the commutating reactor in a dynamic magneticcondition prior to engagement of the electromagnetic switch contacts toallow zero compensation of the current through the commutating reactorat the instant contact engagement takes place.

A still further object of my invention is to provide circuitry for anelectromagnetic rectifier which will maintain the instantaneous contactcurrent during contact engagement at a very low or zero value.

A still further object of my invention is to provide a makepre-excitation circuit which will work in conjunctionwith a conventionalby-passereuit'- suchcthatr'the commutating reactor 'will belunsaturated` before f the by pass circuitV causes contact f engagement;of` ther'electros magnetic switch and the voltage drop across theelectro` magnetic switch at the point at which it yengages will benegligible.

Yet another object of my invention is-to provide a com bination of aby-pass circuit in conjunction with a novel make pre-excitation circuitsuch that themake, pre-excitation circuit will cause unsaturation ofthecommutating reactor after a regulating means allows energization of boththe by-'passr circuit and the make pre-excitation circuit-tosubsequently cause contact engagement under sub; stantially zero voltageconditions...

Electromagnetic rectitiers can use regulators which normally comprise asaturable -type vreactor such. as is shown in co-pending applicationSerial No.- 257,398. After theV regulator is unsaturated to allow theflow of by-pass current, a voltage drop willi appear across the engagingcontacts which is -due to thevoltage' drop on the resistance and airinductance of the parallely connected regulator coil, this voltager dropbeing` the product of the relatively high by-pass circuit current` andthe resistlance and air inductance of the saturated regulator C01 Inmany applications, this voltage drop` can ybecome excessively large andcan eventually cause severe contact deterioration. It was pointed outabove that the presence of a voltage drop across the contacts at lthe,time'of make is 'a severe limitation for electromagnetic rec'tiiers.v By

now using the above-mentioned make pre-excitation circuit as a basicelement of an electromagnetic rectifier, I can now provide a novelcompensation` circLtwhichv will compensate for the voltage drop in theregulatorcoil` due to its resistance and air inductance.'

The principle of my novel compensatingcircuit is to provide an impedancewhich duplicates the air inductance and resistance of the regulatorcoil-and placethis iml pedance in series with the regulator coil. Thisimpedance is now essentially a measuring device which will exactlyduplicate the voltage drop which appears on'the'regulator coil. I thenimpress this voltage upon the primary winding of a transformer andconnect the secondary winding of this transformer in series with thecontacts and the regulator coil, the induced voltage being in a di#rection opposite to the measured voltage. The transformer willfurthermore have an appropriate turns ratio to exactly match the voltagedrop across the measuring circuit and the regulator coil.

More specifically, the secondary winding and theprimary winding of theabove mentioned transformer ca n be connected in series with the valveof the make preexcitation circuit. Hence the voltage acrossv theregulator coil and the measuring impedance will be exactly compensatedby the voltage induced in the secondary windingy of the above mentionedtransformer, andthe total voltage across the contact will beze'ro oravery small value.

Accordingly, another object of my invention is to provide a compensationcircuit to compensate for the voltages' appearing across the contactsduring contact operation which is due to the voltage drop appearing onimpedances which are connected in parallel withA the contacts.

Another object of my invention is to provide a compensating circuitwhich automatically compensates for the voltage drop which appearsacross the saturated regulator coil and is reected across theelectromagnetic switch contacts.

Another object of my invention is to measure the voltage drop due to theby-passV circuit current flowing through the regulator coil and toimpress across the electromagnetic switch contacts a voltage ofv equalamount and opposite phase to` maintain zero'voltage across theelectromagnetic switch contacts.

The maximum `output voltage of -a given electromagneticrec'tier isobtained by closing the` electror'nagnetiev switch contacts at the pointwhere the A.C. voltage is zero and becoming positive in an attempt totransfer the maximum A.C. power of a given polarity to the D.C.4 load.However, after closing the contact at zero voltage there is a finiteinterval of time before the power of the A.-C. source can'be impressedupon the D.C. load. This interval of time is due to the time required toener gize the drive magnet of the electromagnetic switch to therebycause contact engagement and is also due to the time 'requiredtosaturate the saturable transformer and commutating reactor.

This hasbeen overcome in the past by inserting` a D.C. voltage source inseries`with the by-pass circuit to thereby initiate current conductionin the by-pass circuit before the time of zero A.C. voltage andtherefore close the contacts when the A.C. voltage is still at a.negative polarity. The time required for closing the switch andsaturation of the saturable transformer and commutatng reactor will thenbe the time required for the A.C. voltage to assume a zero polarity andthe maximum A.C. power will be delivered to the D.C. load.

A further advantage of decreasing the power factor of the input power isachieved since the reactive voltage. drop is avoided.

However, the use of an additional-DC. source to achieve thisV endvrequires additional power, costly components, increased maintenance,and 4decreases relia-` bility of the over-all rectifier.` The principle'of my invention is to attain the same results'as mentioned above withthe use of a D.C. bias by providing a capacitor in' parallel with thediode in the by-pass circuit. This capacitor will then be charged duringthe interval of timeV in which the electromagnetic switch is open and byproper adjustment will discharge at a predetermined time before thevoltage will decrease to zero.y By discharging this capacitor beforezero voltage, I then initiate a given by-pass circuit current which willallow A.C. power to be transferred to the D.C. source atr the time theA.`C. voltage assumes a zero value and' maximum power can be deliveredat a high power factor for the input power.

It should be noted that the use of a novel' capacitor does noterequireany additional power but merely absorbs a small amount of power from theA.-C. source to beL rectified during the time the A.C. source is atapolarity which is not desired for the D.C. load. A more' practicalapplication of my novel capacitor for pre-energization of the by-passcircuit would require the use of a small diode in series with thecapacitor, connected in a direction to allow discharge of the capacitorin the proper direction before the A.C. source assumes zero voltage anda resistor in parallel with the last mentioned diode which will preventa high inrush current through the capacitor after disengagement of theelectromagnetic switch contacts.

Accordingly, another object of my invention is toprovide means toincrease the maximum output voltage and power factor of a givenelectromagnetic rectifier.

Another object of my invention is to provide a capacitor in the by-passcircuit of an electromagnetic recti fier which is so connected as toinitiate current flow in the'by-pass circuit before the A.C.lsourceassumes zero voltage.

Another object ofmy invention is to'provide a preenergizing capacitor inthe by-pass circuit of an electromagnetic rectifier which is energizedfrom the main alternating power source during 'the portion of the cyclein which the power source will not deliver power to the D.C. load.

Still another object of my invention is to increase the maximum outputvoltage and power factor capable of agiven electromagnetic rectifier" byproviding a preenergizing capacitor' in parallel with the diode of a by@pass circuit, and to provide a parallel connection in series with thecapacitor comprising a second diode and a current limiting resistor toprevent inrush current to the capacitor after disengagement of theelectromagnetic switch contacts.

It is the function of the saturable transformer to shift the currentaway from the current path containing the contact and into the by-passcircuit before the contact break interval occurs. However, the saturabletransformer which has no function at the make must have its uxcompletely reversed during the make process in order to allow its properoperation during the break interval.

In the prior art, an A.C. bias was provided for the saturabletransformer which was so adjusted that the saturable transformer did notaffect the make process and unsaturated for break operation at anadjusted predetermined time. However, this A.C. bias of the prior artcircuitry had to be adjusted to be of the proper magnitude and phase inorder to allow the saturable transformer to operate properly.

This adjustment is a sensitive one and can be a source of considerabletrouble in the operation of a rectifier. I now provide the novel use ofa simple D.C. bias for the saturable transformer in which the saturabletransformer operation at the break will be inherently correct and thesaturable transformer will not in any manner effect make operation withthe exception of a delay in the make process.

The principle of this novel invention is to provide a D.C. bias of apredetermined magnitude for the saturable transformer, and to limit therise of by-pass current during the make process to the magnitude givenby the D.C. bias until the saturable transformer is saturated. Onlyafter the time at which the saturable transformer saturates can theby-pass current then rise to subsequently operate the electromagneticswitch. Although the make process is delayed until the saturabletransformer is saturated, thereby decreasing the maximum output Voltageof a given electromagnetic rectifier, this effect can be easily overcomewith the use of the novel pre-energizing capacitor as mentioned above toinitiate an earlier rise of by-pass current with respect to the inputA.C. voltage.

During the break process, when the total current decreases to themagnitude of the D.C. bias, the saturable transformer will unsaturateand thus effect a shift of the decreasing load current from the maincircuit containing the engaged switch contacts to the by-pass circuit.

Accordingly, another object of my invention is to provide a D.C. biasfor the saturable transformer such that the saturable transformer willnot effect make operation and the saturable transformer will operate atthe break as dictated only by the magnitude of the D.C. bias.

Another object of my invention is to provide a D.C. bias for thesaturable transformer such that the saturable transformer flux will bereversed before the make process can be completed.

As discussed above in conjunction with considerations which must be metto fulll proper rectifier operation, it was pointed out that the movablecontact velocity must be at least inches per second. I therefore proposea novel circuitry which can be used in conjunction with anelectromagnetic switch which can be of the type shown in copendingapplication Serial No. 491,350 which will supply powerful operatingmagnetomotive forces for fast operation of the switch.

In the type of electromagnetic switch having in general an openingmagnetic structure, a closing magnetic structure, a closing coil and aD.C. bias, I propose the use of an additional energizing coil on eitherthe opening or closing magnetic structure which is responsive to theenergization of the closing coil` Hence, if this novel additionalenergizing coil is placed on the openingmagnetic structure, it will beconnected to the closing coil such that energization of the closing coilat the make will cause the additional coil to deenergize the openingmagnetic structure. The subsequent energization of the closing coil atthe break interval will then cause the novel energizing coil to increasethe magnetization of the opening magnetic structure since the potentialappearing across the closing coil will now be opposite to what it wasduring the make interval. kTherefore the additional energizing coil ofmy novel invention provides bucking action of the magnetic flux in theopening structure when it is desired to close the contact and a boostingaction in the opening magnetic structure when it is desired to open thecontact, thereby providing an extremely fast operating electromagneticswitch.

Accordingly, another object of my invention is to provide circuitry toprovide fast action of the electromagnetic switch.

A further object of my invention is to provide an additional coil on themagnetic structure of an electromagnetic switch which is energized inresponse to the energization of the magnetic structure such that themagnetic action due to the magnetic structures will be enhanced for bothopening and closing the electromagnetic switch contact.

Another object of my invention is to provide an additional coil on theopening magnetic structure of an electromagnetic switch which isenergized in response to the closing coil such that it will boost themagnetic action of the opening magnetic structure during the breakoperation and will buck the magnetic action of the opening magneticstructure during the make interval.

In addition to the above mentioned novel circuitry for theelectromagnetic switch, I propose the use of a second novel circuitwhich will give the electromagnetic switch an even more positive actionduring the make and break interval. This novel circuit is based on therealization that the saturable transformer is unsaturated immediatelybefore it is desired to operate the electromagnetic switch.

The principle of my invention is to couple the saturable transformer toan energizing coil of the electromagnetic switch. Hence during the timethe saturable transformers is unsaturated, and has transformerproperties, it will induce a strong voltage pulse into the energizingcoil of the electromagnetic switch to which it is connected. Obviously,more than one coil of the switch can be energized in response to theunsaturation of the saturable transformer.

By properly connecting a coil on the saturable transformer to anelectromagnetic switch coil such as the closing coil, this pulse will bein a proper direction for desired operation of the electromagneticswitch. That is, during the break interval, the pulse induced in theclosing coil by the saturable transformer will be in a direction to buckthe magnetization of the closing magnetic structure.

During the make interval, the pulse induced in the closing coil from thesaturable transformer will be in a direction to boost the magnetomotiveforce of the closing magnetic structure. This operation will beparticularly important at low load currents where the additional pulseswill assure positive operation of the switch inthe absence of highcurrent through the closing coil.

Accordingly, a corollary object of my invention is to provide anauxiliarydriving magneto-motive force to the driving magnet of theelectromagnetic switch which is responsive to the magnetization of thesaturable transformer. Y

Another object of my invention is to provide sharp magnetizing anddemagnetizing pulses to the drive magnet of an electromagnetic switchwhich are responsive to the magnetization of the saturable transformerto thereby provide positive operation of the electromagnetic switch evenunder low load conditions.

Regulators using-magnetic cores for mechanical recti- 9 tiers" achievedregulation `byl pres'etting the magnetic flux of a'saturable reactorwhichis in series with the by-pass circuit. Hence the by-pass circuitcurrentdoes not rise untilfthe-v flux of the. regulator core is overcomeand contact. closure is spbsequently delayed with respect to the phaseof theinput voltage.

In= circuits using a saturable transformer to operate at thetbreak'totransfer current from the main power circuit and: into thebypasscircuit, it is essential that the transfer takes place without any delayif proper break operation is to be achieved. Therefore, if a magneticcorefis'tobe' used as aregulator, I have, foundv that the ux of the coremust not be reset after the. make operation (due tothe collapse ofcurrent in the bypass-circuit after-'the make) or a delay Vwill bepresentedwhen, at the break; current is transferred into the by-passcircuitby the saturable transformer.

I'have been ableto overcome this situation by providinganrv auxiliarywinding for the regulator core which carries the main current. Hence,the total ampere turns which oppose the calibratingDfC. bias (or D.C.winding which determines voltages regulation) is that due to the maincurrent as well as the by-pass circuitv current. Hence,fas' long as thetotal ampere turns of the regulator core is greater than a predeterminedamount, the D.-C. biasl of` the regulator core will not reverse. the uxand the break process will -proceed as if no regulator core werepresent.

Accordingly, a further object of my invention is to'u'se a-regulator ofthe magnetic core type which is inserted. in theby-pass circuit and hasan additional winding which carries the load current. for preventingreversal of' the regulator core ux prior to the contact break interval'.

As was previously mentioned in the stated conditions whichrmust besatisfied for proper operation of an electromagnetic rectiiier, it isessential that the commutating reactor'is so biasedV during itsunsaturated interval for contact protection that the total currentthrough the main windingfand hence the current through thev contactduring the/step be as small as possible. I therefore propose the use ofan A.C. bias supply circuit forthe commutating reactor which provides anA.C. bias having the proper magnitude and proper phase to supply themagnetizing current required by the commutating reactor during both themake and the break. Biases or pre-excitation circuits forthis purposeare well known in the mechanical rectifier arty and the required phaseshift has heretofore beensupplied by conventional phase shiftingtransformers and well? known devices of that type. These phase shiftingdevices' are, however, expensive, largeand difficult to manufacture. Itherefore provide a novel phase shifter for the supply of the A.C. biasof the commutating 'reactor in which both phase shift and magnitude areeasily adjustable.

My novel phase shifter comprises a bridge connected circuit wherein thefirst pair of arms comprise inductors and thesecond pair of armscomprise resistors and the inductors are magnetically coupled. Bymaking-these components variable, it will be shown hereinafter that theoutput will be of easily adjustable phase shift or magnitude.Accordingly, another object of my invention is to provide a vnovel phaseshifting device for the supply of the commutating reactor A.C. biashaving an easily adjustable phase shift and magnitude.

Stillanother object of my invention is to provide a novel phase shiftingdevice comprising a bridge connected circuit having inductors inthelirst pair of branches, resistors in the second pair of branches', andmagnetic coupling between the inductors of the first pair of branches.

These and other objects of my invention will now be comeapparent fromthe following descriptionwhenV taken iii connection with the drawings inwhich: A

Figure 1 shows theV basic circuit of my invention as' a single phase`half-wave rectifier and` contains the-coms ponents which must be basicto any electromagnetic'rectiier.. Thatv is,Figure l showsV thepower`source a D.SC. load, an electromagnetic switch, a saturabletransformer, a1 commutating reactor, a by-pass circuit, a regulator(which is not a basick element), and the novel make preexcitationcircuit which I have described as a new basic element for anyelectromagnetic` rectier.

Figure 2y is the same as Figure l butr isy extended tofu single phasefull wave rectifier.v

Figures 3a to 3h show the voltage or currentf characteb istic's of thevarious components of Figuresl and 2 as plotted'against a common timebase.

rFigure 3a shows they voltage current characteristic as plotted againsttime of the voltage source.

Figure 3b shows the voltage characteristic plotted. against time ofthesaturable transformer main winding.

Figure 3c shows the voltage time characteristic-of the commutatingreactor main winding.

Figure 3d shows the voltage time characteristic ofv an inductor'in theby-pass circuit.

Figure 3e shows the voltage current characteristic'. plotted againsttime for the electromagnetic switch contact.

Figure 3 f shows the voltage and current plotted against time for theregulator coil winding in the by-pass circuit.y`

Figure 3g shows the load voltage plotted against time;` and Figure 3hindicates the common time base for Figures 3a through 3g.

Figure 4 shows the basic circuit diagram of Figurel l taken inconjunction with my novel compensation circuit which will compensate forthe voltage drop acrossthe electromagnetic switch contacts due to thevoltage drop on the parallel connected by-pass circuit regulator coil;

Figure 5 shows the basic circuit of Figure l taken iri conjunction withmy novel feature of a preenergized by# pass circuit to compensate forthe overall voltage drop of the rectifier and thereby increase themaximum voltage output and power factor of a given electromagneticrectiA fier.'

Figure 6 shows the f basic circuit of Figure l when taken in conjunctionwith the novel auxiliaryy winding which is energized from the closingcoil of the switch to' provide faster make and break operation oftheelectromagnetic switch.

Figure 7 shows the basic circuit of Figure 1 and shows the novelconnection of the closing coil and saturable reactor to thereby providestrong opening and closing pulses for the electromagnetic switch.

Figure 8 shows the basic circuit of Figure l with an A.C. bias on thecommutating reactor as supplied by my novel phase shifting circuit.

Figure 9 shows a vector diagram of the operation of my novel phaseshifting circuit.

Figure 10 shows the basic circuit of Figure l when taken in conjunctionwith the novel features shownV in Figures 4 through 9.

Figures 11a through 11j show the voltage current characteristics of. allof the elements of Figure 10 as plotted against a common time base. y

Figure 11a shows the current and voltage characteristic of the voltagesource.

Figure 11b shows the voltage time characteristic of the electromagneticswitch contacts.

Figure llcshows the voltage and current time characteristic of theoperation of the saturable transformer main winding and the saturabletransformer winding lying in the by-pass circuit.

Figure 11d shows the Voltage time characteristic of the commutatingreactor main winding. l

Figure 11e shows the current-voltage characteristic` as plotted againsttime for my novel capacitor which is used to pre-exciteby-pass circuitcurrent to thereby 'allow maximum output voltage and power factor foragiven rectifier.

Figure llf shows the voltage-current characteristic as plotted againsttime for the by-pass circuit.

Figure 11g shows the voltage time characteristics of both the loadvoltage and the voltage appearing on the regulator coil winding in theby-pass circuit.

Figure 11h shows the current time characteristic of both the totalcurrent owing through the closing coil of the electromagnetic switch andthe current fiowing through the saturable transformer winding which iscoupled to the closing coil of the electromagnetic switch.

Figure lli shows the current time characteristic of the current flowingthrough the novel auxiliary winding on the electromagnetic switch whichis coupled to the closing coil. Figure 11j indicates the common timebase for each of Figures lla through 1li.

Figure l2 indicates the extension of the basic circuit of Figure 1 andeach of the novel features specifically shown in Figures 4 through 8 asapplied to a three-phase half wave rectifier.

Basic circuit including make pre-excitation The basic circuit whichcomprises all elements which are essential in an electromagneticrectitier are shown in the circuit diagrams of Figures 1 and 2. Itshould be noted that the circuit of Figure 2 is identical with that ofFigure 1 with the exception of its being a full wave rectifier. Itsdescription and operation will therefore be exactly the same as thefollowing description which will be taken in conjunction with Figure 1.

In Figure l the basic components are shown as an A.C. power source orgenerator 10, a D.C. load 11, a drive magnet which comprises a closingmagnetic struc- -ture 12, a closing coil 1.3, an electrically conductivearmature 14 which is operated into and out of engagement responsive to amagnetic iield and an opening bias which is shown in Figure l as abiasing spring 15. It is clear that the spring 1S could be replaced byany other type of biasing force such as another magnetic structure. Ifdesired, the armature 30 could be shown as being biased closed and astructure such as magnet structure l12 could operate to defeat theclosing bias.

A further basic component is shown as a saturable transformer 16 whichcomprises a core 17, main winding 18 which is in the main current path,a biasing winding 19, and a winding 20 which is situated in the by-passcircuit. The saturable transformer D.C. bias is impressed upon winding19 from a positive terminal 21 and a negative terminal 22. It should benoted that the use of a D.C. bias for the saturable transformer 16 isnovel yas was shown above and as will be described more fullyhereinafter and that this bias could be of the A.C. type used inelectromagnetic rectifiers of the prior art.

Still another basic component is shown as a commutating reactor 23 whichcomprises a main winding 24 and :an iron core 25 which, similarly to thecore 17 of saturable reactor 16, is made of easily saturable material,such as Permeron.

The by-pass circuit which again is a basic element in anyelectromagnetic rectifier is shown as being in parallel with theelectromagnetic switch contact 14 and comprises the `series connectionof the saturable reactor winding 20, diode 26, inductor 27, andregulator coil winding 28.

Although the regulator is not considered to be an esseri-tial elementfor an electromagnetic rectifier, it has been included in Figure lbecause of its practical importance in a commercial rectifier. Morespecifically, regulator 29 is shown as comprising the above mentionedwinding 23 and a biasing winding 30 which affords voltage control of therectifier output voltage by varying the D.C. bias impressed upon winding30 from the D.C. terminals 31 and 32. As further shown in Figure l, the

main D.-C. conductor comprises -a winding of the regulator core 33 formaintaining forward saturation as long as the current flows throughcontact 14.

It should be noted that all of the above mentioned basic elements areold, with the exception of the novel regulating system. As mentionedabove, I now propose the use of still another basic element which isrequired for the successful operation of any electromagnetic rectifier.This basic element comprises the novel make preexcitation circuit shownas diode 34 which is connected in series with the commutating reactorwinding 24, the regulator winding 2S and in parallel with theelectromagnetic switch contact 14.

In the absence of a regulator, the diode 34 would be connected directlyin parallel with the electromagnetic switch 14. However, as will beshown hereinafter, this is essentially the case since the regulator core33 will be saturated at the time contact 14 is closed and the makepreexcitation is required. That is, even with the presence of aregulator, the make pre-excitation circuit is connected directly inparallel with the electromagnetic switch contacts during the time ofcontact operation.

It should be further noted that although I show my make pre-excitationcircuit as comprising a semi-conducting diode 34, that this diode couldbe replaced by any electronic valve or by any circuit element having anasymmetric impedance characteristic.

The operation of Figures 1 and 2 is now taken in combination with thevoltage current characteristics as plotted against time in Figures 3athrough 3h for one full cycle of operation. VIt should be noted that inthe Figures 3a to 3h the common time base shown in Figure 3h has beenexaggerated for a clearer understanding of the circuit operation.

As seen in Figure 3a at the time t0, the voltage e10 of generator 10becomes positive and initiates a current through the circuit13-18-20-26-27-28-11. But because the core 33 of theregulator-transductor 29 is not saturated, the coil 28 has an almostinfinitely high impedance, thereby preventing the current Ito rise to anappreciable value.

The voltage eli) therefore appears on the coil 28, shown in Figure 3 fas the voltage e28. The same voltage appears as e14 across the parallelconnected contact `14 as shown in Figure 3e.

Between the time ttl-t1, the voltage time integral shown in Figure 3f asthe triangular area under the voltage e28 is applied to the coil 28 andcauses a change in the magnetic flux of core 33. At the time t1, themagnetic flux in the core 33 has reached saturation value, whereuponcore 33 saturates and the impedance of winding 28 drops to a very lowvalue. Hence the voltage e28 across the coil 28 disappears suddenly, asshown at time t1 in 3f. The current 1'28 (or i27) immediately starts torise, because the generator voltage el() of Figure 3a no longer isopposed by the voltage e28 on coil 28. The generator voltage e10 nowappears on the largest impedance in the circuit which is thecurrent-limiting choke 27 and is shown as the voltage e27 in Figure 3d.Due to the limiting action of choke 27, the current i27 rises graduallyafter time t1, as shown in Figure 3 f.

It should be noted that the currents i27 and i28 shown in Figure 3f aredrawn at a much larger scale than the generator current :'10 of Figure3a or the contact current 14 of Figure 3a. Therefore, in the timeinterval t1-t5, the currents i27 and 1'10 are equal, and the largerappearance of i27 in Figure 3f as compared to 1'10 in Figure 3a is dueonly to the different scales.

When the voltage e27 of Figure 3d rises suddenly at the time f1, thesmall rectifier 34 of my novel make preexcitation circuit conducts acurrent which tiows through the winding 24 of commutating reactor 23.Because the core 25 of the commutating reactor 23 is not saturated, theimpedance of winding 24 is extremely high, thereby limiting the currentthrough winding 24 and annesse diode-34 toa very low value. The voltagee27 thus also appearson the coilr 24, shown as e24.in Figure 3c. Withthe coil 24 assuming the voltage-drop shown in Figure 3c, there remainsbut little voltage e14 across the switch 14, as shown in Figure 3e.Actually after t1 and until the switch 14V closes at` t4, the voltageacross it is very low, given only by the resistive and inductive dropcaused inl the coil 28 by the current i27. Aswill be shown hereinafter,I shall provide a. circuit to compensate for this additional voltagedrop which appears across contact 14.

Therefore, by the simple application of a small' rectifier 34 whichcomprises my novel make pre-excitation circuit and introduces a newvbasic component for electromagnetic rectiers, the voltage across theswitch 14 is almost zero for an interval beginning before and endingafterfthe switch 14 actually closes.

During the time t1-t2, the core 17 of thesaturable transformerremainssaturated -bythe direct cu-rrent premagnetization supplied bythe: coil 19 which is fed from a D.C. supply 21--22. The novel use of aD.C. bias for the saturable transformer will be explained hereinafter ina more complete manner in conjunction with Figure 6., At the time t2,the current :'27 of Figure 3f owing through saturable reactor mainwinding 18 and saturable reactor by-pass winding 20 equals'the action ofthe `direct current in winding 19 and the core 17 unsaturatesi.- A highimpedance then appears on the coils 18 and 20 which assumey the fullgenerator voltage e10, as-shown in Figure 3b. The level of the directcurrent i1,9^ at whichthis happens, is shown in Figure 3a, as comparedto the generator current i10. The voltage e27 on choke 27 disappears,since the current :'27 is prevented from further rise by the action ofthe coils 18 and 20.

In the time t2l3, the voltage e18 appearing on the coil 18 effects acomplete flux-reversal inV the core 17. During the time t2-t3, thevoltage e24 on the commutating reactor coil 24 is kshown in Figure 3c asbeing reduced to a lower value because the generator voltage is nofwapplied to the coils 13 and 20 in series.

Atthe time 1,3, the core 17 of saturable ,reactor 16 is saturated in adirection Vopposite to its saturation before t2, and thereafter thecurrent 1'27 continues to rise as before.

At .the time t4, the current 27, flowing through 1 3j-18-20.-26`-272811has risen to such a value that therswitch 14 is closed by the magneticaction of theiron ncoref12 which is magnetized by the coil 13. Actually,the magnetomotive force for statically closing the electromagneticswitch is attained at an earlier time, for example, t3, but a certaintime is required for the armature to travel the. full closing distance.The voltage e14vacrossthe switch 14 now collapses to zero, becausetheswitch closes, but this final collapse concerns only averysmall-voltage as` shown in Figure 3e. Before closing, the `small voltageappearing across the switch is dueto thevoltage drop in the aircorereactance of the coil-28` (the ironcore 33Y being saturated at l1) andthe ohmic resistance of the winding 28 submitted to the currentv 127,shownl in Figure 3 f.

When theswitch 14 is closed, there is no change in thebehayiorofvoltages and currents in the circuit. As before, the` generator voltagestill appears on the commutating reactor-winding24, shown as e24 inFigure 3c, on the parallel choke. 27, shown as e27 in Figure 3d. Becausetherev is-novoltage on the switch 14 while it closes, there will be noinrush current. The only current `flowingthrough, 14 would come from thecommutating At the time t5, the core A251ina11y saturates, and thereforether-impedance` of' the coil'2i4 suddenly' vanishes The voltage e27 onchoke 27, which is in parallel with the coil 24, vanishes also and thegenerator voltage e10 which until time t5A was. applied to' the'rectiersystem, suddenly appearsonthe load' 11 as e11 shown in Figure 3g; Thecurrent 1'14 through the electromagnetic switch 14 (shown in Figuree)increases suddenly, and hence the current 10 is delivered by thegenerator 10 to the load 11 (shown ink Figure 3a). Note that a smallamount of current :'10 ows in the time interval t1--t4, this is nothingbut the current :'27 flowing through the by-pass circuit as shown inFigure 3f. After t5, the current :'27 deca-ys slowly according to ltheinductance-resistance charaoteristics of theby-pass circuit. A decayingvoltage appearson choke 21'as shownv as voltage e27 in `Fi'gl'ireSdwhich reflects theV decay ofthe current i27 of Figure 3f.

The voltage e11 appears on the load 11'as a rectified sine wave with itsbeginning point at t5, delayed vfrom the theoreticalfpoint t0 and itsending point t7 delayed from the theoretical point t6. Due to thisdelayg'the average direct voltageoutput is less than the highesttheoretical average. This is mainly due to the deliberatedelayintroduced by the transductor-regulator coil 28 and its core 33.

Varyingl the control current of the transductor control 30 will varytheamount of ilux displaced by it, hence the amount of flux which has to bedisplaced in the opposite direction by the generator voltage e1() whenappearing on the coil 28 as e28y in the time interval t0- t1; ByV thismeans, the outputvoltage of the rectifier canA be controlled easily witha control current whichy is very small'.

In order to preventeareversal of the flux in the core 33 during the timet5 to t7 when current flows through the switch 1'4 and not through theby-pass 20-26-27--- 28; the core 33 is situated around the mainconductor which leads the rectifier to the D.C. load 11.

When compared vto my copending application VSerial No.` 257,398, theabove-describedr procedure is essentially dierentfor the operation ofthe commutating reactor andthe saturable ytransformer atV the Make.However', the operation ofthe-electromagnetic switch and of theregulator-transductor` remain unchangediin principle. Operation at theBreak is almost unchanged from before and is vas vfollows:`

, In Figure 3a, when the generator voltage'el'becomes zero and reversesits direction at the time t6, the current iI01in^generator and loaddecreases towards zero. At the'time t7, this voltage has reached thelevel of 1119 shown'in Figure 3a or more specifically, the ampere turnsof 1'10 in the coil llbecome equal to the ampere turns of the directcurrent 1'19 in coil 119. Therefore, the core 17 suddenly unsaturatesand its impedance changes from an almost zero or negligible value toalmost infini-te value, i.e. a value larger than any other impedance inthe circuit.

Suddenly the voltage 619 of the generator 10 is applied to this highimpedance coil 18, shown as elS in Figure 3b. The voltage e1`1 on theload 111 disappears at the sameY instant. For the short time t7-t3, thegenerator voltage remains, applied to the coil 18 as shown in Figure 3b.This voltage is transformed into the secondary coil 20 of the saturabletransformer having the core 17. The secondary circuit is closed through'29-26--27--2S- 1424`-20 (diode 34 is opposed to the voltage), and acurrent starts to rise due to this voltage. This circuit containsalmostno-impedance because core 33 is still saturated from the forwardcurrent flowing through the main line until 17, and the commutatingreactor core 2S isstill` saturated fromthe` same current liowing through24. Thus the current 27 startsto rise again as shown in Figure 3f, theonly impedance being the choke 27 which, limitsthe rate of rise ofthecurrent 1`27, while subjected: tor the voltage.. transformed from fWinding 18 15 into winding 20. Figure 3d shows the transformed voltagepulse as applied to the choke 27 as e27.

At a time between t7 and t8, the by-pass current i27 has reached thevalue of the main current at t7. That is, the total main current is nowdisplaced into the by-pass and residual main current through the switch14 and the coil 24 shown as i14 in Figure 3e reaches zero. A furtherincrease of current i27 which would mean a reversal of the current 14,is prevented by the commutating reactor coil 24 and its core 25 whichunsaturates as soon as the line current 1'14 reaches zero or a valuealmost equal to zero.

At the time t8, the switch current i14 is zero and the by-pass current127 is equal to the line current 1'10 and the core 17 of the saturabletransformer saturates thereby ceasing transformer action between thecoils 18 and 19. Generator voltage el() which appeared on the coil 18tends to reverse the current of the coil 24 but this is prevented by theextremely high impedance of the coil 24 and elli now appears on the coil24 and is shown as e24 in Figure 3c.

Current through the switch 14 is limited by the amount of current passedby the commutating reactor coil 24 (the semi-conductor 34 is notsubjected to an appreciable reverse voltage at the time, and passespractically no current), this current being shown as z`14 after t8 inFigure 3e. By proper design and biasing methods, this residual current,flowing through the switch contacts immediately before opening, can bemade extremely small (approximately 1,6 000 of rated line current orless). When the switch opens at the time t9 in Figure 3e, the currentinterrupted by the switch is of such a small amount as. to be of noimportance. After opening, the small residual current can flow throughthe parallel path formed by the rectifier 34 and the coil 28 which has avery low impedance at that time and because the residual current ow isnot restricted, the recovery voltage across the contact is very low, asshown by e14 after t8 in Figure 3e.

By-pass current 1'27 decays slowly after t8, depending on theresistor-inductor constants of the circuit. This is shown as 27 inFigure 3f. Whenever 27 reaches zero, its reversal is prevented by therectifier 26. Hence the by-pass current stops naturally, Withoutreversing. Total load current owing through the rectifier is shown as 10in Figure 3a, its slow decay being a small current (after t8) which isprovided by the by-pass current i27.

At the time t1() the commutating reactor core 25 is saturated, and thevoltage on coil 24 collapses. Generator voltage e110 shown as e14 inFigure 3e now appears on the open switch which has opened to asufficient distance to withstand the high voltage.

When the current 1'27 (or i28) has reached zero, the control current inthe coil 28 reverses the flux in core 33 causing the inverse voltage e28to appear at time r11 in Figure 3f. At the time i12 another identicalcycle begins.

Merits of basic circuit Electrical problems as stated above will be usedto evaluate the merits of the basic circuit point by point.

Condition l. Satisfied, because the contact voltage e30 is loweredsubstantially before the switch starts closing.

Condition 2. Partially satisfied. In critical cases additionalcompensation is required to overcome the Voltage drop of the coil 36which might be sufficient to cause a field discharge. The abovedescribed circuit however is a great improvement over previously usedcircuits.

Condition 3. Satisfied.

Condition 4. Not always satisfied. The complete circuit as described inthe following, does satisfy this condition.

Condition 5. Satisfied to a much larger extent than by previously usedcircuits and the complete circuit will still show a further improvement.

Conditions 6, 7, 8, 9, 1l) are satisfied as they were in the previouslydescribed circuits. These conditions depend mainly upon the quality ofthe core material of the commutating reactor and the compensation of themagnetizing current by means of the pre-excitation which can beaccomplished by careful design and manufacture of all parts.

Condition 11. Not always satisfied. The complete circuit howeverprovides correct operation.

Conditions 12, 13, 14. Satisfied with adequately designedspark-suppressor circuit as will be described in the complete circuit.

Condition 15 is satisfied. This is very important.

Conditions 16 and 17 are not satisfied by the basic circuit but will besatisfied by the complete circuit.

Conditions 18 and 19. Satisfied.

Saturable transformer D.C. bias The novel use of a D.-C. bias for thesaturable transformer is shown in Figure 1 and comprises the D.C. source21-22 and coil 19 on the saturable reactor core 17. As was described,with reference to the above description, the flux reversal of core 17introduces an additional delay in the closing operation without anyapparent result. This, however, is done purposely because the samesaturable transformer 16 must control the operation of the rectifierduring the break interval. Unless the flux of saturable transformer 16is completely reversed during the make process, the break will nothappen correctly, or, inversely, when the make is not accomplishedbecause the current i27 rises insufficiently then no break is requiredand saturable transformer 16 does not operate at all. The abovedescribed operation is a great advantage over the previously describedcircuit in which an A.C pre-magnetization of the saturable transformerwas required. In the prior art devices, unless the A.C.pre-magnetization is correct in amount and in phase, the operation willnot occur correctly. Therefore, the necessity of supplying an accurateA.C. pre-magnetization has been eliminated without any detrimentaleffect upon the system, except the additional delay in the makeoperation. This delay however can be compensated by the output voltagecompensating device which Will be more fully described hereinafter withreference to Figure 5.

Compensation for regulator coil voltage drop As was mentioned in thedescription of the basic circuit of Figure l, an additional voltage dropappears across the contact 14 during the make interval due to theby-pass current i28 owing through the regulator coil 2S of the saturatedregulator core 33.

Referring now to Figure 4, I show a circuit which will provide acompensation for this voltage drop during the make process inconjunction with the basic circuit of Figure 1. As previously mentioned,during the make process a relatively high current flows through theparallel circuit 20-26--27-35 and 28. The voltage drop appearing acrossthe coil 28 also appears across the contact the contact 14. For highcurrent application, this voltage drop might become excessive and causeeventual destruction of the contact 14. The application of my novelcompensation circuit depends upon the introduction of the variableresistor 35 and the transformer 36.

lf the resistance of resistor 35 and the inductance of the choke 27 arethen made proportional to the resistance and inductance of coil 28, andthe transformer 36 is made with a ratio of numbers of turns equal to theproportionality between resistor 35 and inductor 27 as compared to theresistance and inductance of regulator coil 28, then the voltage dropacross resistor 35 and choke 27 is proportional to the voltage dropacross the coil 28. This voltage drop is then impressed upon the primarywinding of transformer 36 and transformed into the secondary winding oftransformer 36 in such a way that the total voltage and the circuit 14,28, secondary of 36, 34, and back ,to 14 is practically zero.

.T17 It ldesired transformer' can be provided with Lan adjustable tap topermit the establishment of a :practical zero point by experiment.v'Similarly induc'tor 27 can be made variable and the impedance ofregulator winding be easily matched (as a ratio) by adjusting thevariable components fof the circuit.

Compensation of the voverall .rectifier voltage drop As was previouslyindicated, the major "cause of voltage drop in an electromagnetic4rectilier from its maximum value is due to the delay in closing of theContact, or make delay. This delay is due mainly to 'the time required'to magnetize the drive magnet, saturable transformer and commutat'ingreactor.

As the magnetization of these 'components can 'be accomplished by acurrent flowing through the vby-pass circuit, a voltage source insertedinto this by-pass circuit, thereby causing the by-pass "current to startbefore the generator voltage rises, would greatly shorten the delay orrender it nil. Hence a ysmall auxiliary voltage source would increasethe voltagev output Aof the whole power system.

In Figure 5, I show a novel means to accomplish this pre-exciting of theby-'pass circuit in conjunction with the basic circuit of Figure 1. InFigure 5, the auxiliary voltage source is the capacitor 37 which scharged each cycle by the 'inverse voltage appearing across the contact14. The power of the auxiliary voltage supply therefore comes from thegenerator itself. When the voltage of generator 10 .is negative, nocurrent can ow through the rectifier proper since each path 'of currentow has a blocking element. However, by providing la small resistor 38 inseries with capacitor 37, a small current can flow to thereby charge upcapacitor 37 positive below and negative above. When the negativevoltage lof generator 10 decreases there rcomes a point where thenegative voltage of capacitor 37 becomes larger than the voltage ofgenerator 10. Under this condition, a positive current will now owthrough the by-pass circuit from capacitor 37 to diode 39, 27, 28, 11,10, 13, 18, and back to capacitor 37. This means that the make processis initiated before the time at Which the generator voltage becomespositive. Therefore, the make will happen earlier and the voltage outputof the rectifier will be higher.

Auxiliary winding drive for the drivemagnet Figure 6 shows schematicallya complete electro magnetic switch of the type described in U.S. PatentNo. 2,805,300 issued September 13, 1957 in conjunction with a novelauxiliary winding for positive contact operation. The rectifiercircuitry is that of the basic circuit shown in Figure 1.

The electromagnetic switch of Figure 6 now comprises a closing magneticstructure 40, an opening magnetic structure 41, a biasing coil 42 forthe closing magnetic structure and a biasing coil 43 for'the openingmagnetic structure. The biasing coils 42 and 43 can be supplied from acommon D.C. source showing the terminals 44 and 45. I now provide anovel auxiliary winding 46 which is energized through the resistor 47 inresponse to the energization of closing coil 13. Note that closing coil13, resistor 47 and auxiliary coils 46 comprise a closed electricalcircuit.

The operation of this novel drive system is as follows: When the closingcoil 13 is energized before and during the make process, a relativelyhigh voltage drop appears across it. A current proportional to thevoltage then flows through resistor 47 and coil 46 in such a directionas to counteract the effect of bias winding 43 on the opening magneticstructure 41. Hence during the make proce ess, the opening magneticstructure 41 is demagnetizet. while the closing magnetic structure 40 ismagnetized.

Inversely, immediately before and during the break, the closing coil 13is once again demagnetized, Vthereby .requiring a voltage drop across itin 'a reverse direction than fthe make. This reverse voltage drop causesan opposite current to flow through resistor 47 and coil r446 which nowboosts 'the action of bias-ing winding 43 thereby resulting in a stron-gmagnetic field of the opening magnetic structure 41 while the closingmagneticstructure fis *demagnetfized "'lt should he noted that thecurrent flowing in the short circuitcomprising closing coil 13, resistor47 and auxiliary winding 46,v is damped down to zero by the action ofresistor 47. Different damping constants can be obtained by 'simplyadjusting the value of resistor 47 to obtain rthe desired Abuck-boost'action in the drive magnet structures.

i Saturable vtransformer drive for the drive magnet The saturabletransformer 16 in Figure 7 is shown having an auxiliary winding 4S whichis coupled to the closing coil 13 of the drive magnet through a resistor49 and inductor 50. Since the saturable transformer 16 is unsaturatedimmediately before the make and unsaturated n the opposite direction`immediately before the break, a voltage will then cause a current toflow through vthe circuit comprising the coil `48, inductor 50, resistor49, 'drive magnet closing coil 13, and back to winding 48 to therebyprovide a strong magnetization of the closing structure through the coil13 at the make and a strong demagnetization of the Aclosing structurethrough the closing 'coil 13 at the break.

Inductor 50 and resistor 49 merely limit these closing and openingcurrent pulses and maintain them long enough to ensure a powerfuloperation. It is obvious that by the addition of this small auxiliarycircuit, a powerful magnetizing pulse and a powerful demagnetizing'pulse is sent through the drive magnet closing structure whenever theswitch should close or open respectively. This will be particularlyimportant at small loads where the additional pulses assure positiveoperation of the switch. Whenever the current rises to a value less thanthe level of the bias in the saturable transformer Winding 19, theclosing and the opening pulses will cease and in this case the drivemagnet will not be sufficiently energized to operate contact 14.

Phase shifter for the commrumting reactor A.C. bias Figure 8 shows thebasic circuit of Figure 1 wherein an A.C. bias for commutating reactorcore 25 is supplied from a novel phase shifter which supplies an A.C.bias of proper phase shift and magnitude. Since 'commutating reactor 16has a core 25 of highly saturable iron, the cornmutating reactorrequires a very small but non-negligible current to magnetize it in aforward or reverse direction. During the make step, the magnetization isin the forward direction, hence the magnetizing current is also in theforward direction.

The use of the highly saturable magnetic material, that is, a magneticmaterial having a square hysteresis loop will make this magnetizingcurrent practically constant. Hence if a current of almost constantmagnitude is impressed upon the bias winding 51 it will compensate atleast partially for the m-agnetizing current, Similarly during the breakstep, the magnetization occurs in the negative direction, hence themagnetizing current is negative. If the current n auxiliary coil 51 isalso negative at this time, it will compensate at least partially forthe negative magnetizing current. Therefore by `adequate adjustment ofthe A.C. current owing through the coil 51 in both amount and phaseangle together with the proper number of turns which is determined fromthe D.-C. bias coil 52 will make it possible to have a very low residualcurrent during both the make and break nn.tervals. It should be notedthat both of these residual currents will be slightly positive while themake and break step still occur at the right time and that the bias doesnot initiate these steps at an unwanted time.

Adjustable amplitude and phase angle of the A.C. bias y with respect tothe inpart voltage is obtained in Figure 8 by means of the novel phaseshifting circuit comprising the inductor 53 and the phase shifterelements comprising the double inductor 54 and resistors 55 and 56..

The purpose of choke 53 is to prevent pulses which are generated in lthecommutating reactor auxiliary winding 51 `from being i-mpressed into thephase shifter circuit.

Operation of `the phase shifter circuit of Figure 8 is more speciticallydescribed by the vector diagram of Figure 9. Referring now to bothFigures 8 and 9, the vector el() represents the voltage of generator 10.A phase shifter network is connected across the generator voltage andconsists of the two coil reactor and resistors 55 and 56. Current owinginto the phase shifter is represented by the vector :'10, in Figure 9.

Since the circuit is resistive and inductive, the current :'10 lags thevoltage @10. e54L is the Voltage across the left hand coil of reactor 54in Figure 8 and e54R is the voltage of the reactor on the right handside of component 54. Due to the transformer effect, these voltages willbe equal. Furthermore, the reactor 54 has an iron core with anadjustable air gap to thereby permit the adjustment of the reactance ofthe coils comprising the reactor 54.

Figure 9 further shows the vector voltages c55 and e56 as representingthe voltages appearing across resistors 55 and 56 in Figure 8. From thecircuit diagram it is obvious that:

(1) e1o=54n+e55 (2) e1o=e54n+e56 Referring again to Figure 9, the upperdiagram shows vthe vectorial addition of these voltages. It is shownthat resistor voltages e55 and e56 are equal and in phase and that thereactor voltages e541, and em are also equal and in phase. The reactorvoltages, however, are shown as leading the resistor voltages.

Referring now to the lower portion of Figure 9, the current additionsare shown as:

Since the resistors 55 and 56 are considered to be practicallynon-inductive, the vectors :'55, e55 and :'56, e55 are parallel, therebyassuming that they are in phase. Since the reactor 54 is considered tobe practically non-resistive,

it will be observed that vectors e54L, i541, and e54R, 54R

This can also be obtained by subtracting the vectors 1n the upperdiagram of Figure 9. Similarly, the output current of the phase shifteris determined from the rela tions:

frs

vector relationships. Since choke 53 is assumed to have a negligibleresistance, the voltage e53 which falls across it will lead the current:'53 by 90. The phase shift angle between the input voltage and outputcurrent is now shown in Figure 9 according to the above relationships.By varying respective values of resistance for contact reactance or byvarying both resistance and reactance together will clearly allow anyphase shift or output magnitude which is desired.

Operation of the complete circuit A complete electromagnetic rectifierwhich will satisfy all of the conditions presented heretofore for asuccessful electromagnetic rectifier is shown in Figure l0. It should benoted that Figure 10 is exactly the same as the basic circuit of Figurel plus the additional features shown in each of the Figures 4 through 8.The operation of the complete circuit of Figure 10 will be described incombination with the voltage current characteristics of its variouscomponents as plotted against time in Figures lla through 11j.

Although the operation of the circuit is essentially identical to thebasic circuit of Figmre 1, the changes which are introduced due to theadditional features change the voltage time and current timecharacteristics suiciently to necessitate an additional description.

It should be noted that all of the features mentioned heretofore havebeen in the circuit of Figurev 10 but it vshould be noted that thevarious features could be used singly or in any combination in a givencircuit.

As will be seen when referring to Figure 10, the D.C. supplies requiredby the various components is supplied from a common source 60 which hasa smoothing choke 61 in series therewith.

Furthermore, for easier representation of the operation before and afterto or the time at which the generator voltage assumes a zero value,Figure l1 is shown with the cycle split immediately before -l-G and notat t0 as was done in Figure 3. Due to the compensation for the overallvoltage drop, the actual closing procedure is for the case of Figure l0initiated before to. The times preceding that at which the generatorvoltage assumes a zero value are indicated by the times L3, t 2, and f lin vFigure 11j.

The following table indicates comparative times at which the sameoperations occur for the circuit of Figure l as shown in Figure 3 andfor the circuit of Figure 10 as shown in Figure 11.

Operation Fig. 8 Fig. 11

Begin sat. transformer action Make ABypass circuit current reacheszero.-

Zero generator voltage, increasing Begin regulator action End regulatoraction End sat. transformer action Make.

ke step Zero generator voltage, decreasing... Begin of sat. trans.action break Contact current reaches zero. End of sat. transf. actionbreak Begin of break step Break (opening of contact).

End of break ste Begin ux reversal regulator coil End ux reversalregulator coil Similarly, as was done in Figure 3, the time intervalshave been exaggerated as compared to the duration of the whole cycle foreasier understanding of the diagram.

Make process for complete circuit of Figure 10 :as e2.; in Figure llfwhich is equal to generator voltage ew in Figure 11a. The same voltageshown as eas in Figtire llf also appears on the small rectier 39 andresistor 38 because the capacitor 37 is unc-harged. Due to this voltagea small current :'3q of Figure lle flows through the resistor 38,causing a charging voltage esq on the capacitor 37 as is also shown inFigure lle. The reverse voltage e110 follows the generator voltage @10of Figure lla and the capacitor voltage esq, shown in Figure llf as adotdash line, gra-dually increases with the rate of increase given byresistance of resistor 38. At the time 1 3, the capacitor voltage esqequals the reverse voltage e26 and after t-3 will be even larger.

After time t3, a voltage is impressed in the circuit10-1318-20-37--39--27-35-28-11-10 due to two sources, the impressedvoltage e10 of the generator and the stored voltage e3q of thecapacitor. The sum of these two voltages, shown by the dotted line whichindicates e10+e3q in Figure llc, is positive because esq is larger thanelo, and therefore a positive current starts flowing through thiscircuit. This is equivalent to a generator voltage turning positive atthe time t-3. Current rising in the by-pass circuit is shown as dottedline 20 in Figure llf.

Between the time t-3 and t-Z, the by-pass current :'20

:is limited by the regulator coil 28, the core 33 of which must besaturated in the forward direction before it passes an appreciablecurrent. Flux reversal of the core 33 was previously accomplished byreverse current in coil 30 d'uring time t13-t1-4 and is shown by thereverse voltage e28 which is the dotted line of Figure llg. Flux changein the forward direction is accomplished by capacitor voltage e3qappearing between t-3 and t-2 -on coil 28 as egg in Figure llg.

The example shown in Figure l was purposely drawn for a case with Verylittle regulation of the voltage. Hence, the lluX reversed in core 33 isvery small and the delay time t-3 to t-2 is very short. For lowervoltage output, this delay can be increased by any desired amount.

At the time t-Z, core 33 saturates and by-pass current 1'20 rises freelyas shown by the dotted line in Figure llf. The by-pass current isequivalentto capacitor dischargecurrent :'0q shown by the dotted line ofFigure lle and to current in the main line :'10 which is shown by thedotted line in Figure lla during this part of the cycle.Discharge-current :'3q causes decrease of capacitor voltage esq as shownin Figure lle.

When the by-pass current :'20 of Figure llf, ows through coils 18 and 20in series, it reaches a value equivalent to the D.C. bias current incoil 19 at time t-1 and core 17 of the saturable transformerunsaturates. This is identical to the operation described for the basiccircuit. The by-pass current :'20 is now maintained constant vby thesaturable transformer as shown in Figure llf.

The sum of voltages in the circuit, which are e and eaq and are shown asa dotted line in Figure llc` is applied to the saturable transformer,and is shown in Figure llc as @18d-e20- Voltage suddenly appearing oncoils 18 and 20 at time t-1 is transformed into coil 48, giving rise toa circulatory current L18 (dotted line in Figure llh) in the closed loop48-50-49-13-48- Circulatory current :'.10 is added to previous current:'20 in coil 13, as shown in Figure lll: by the sharp rise of :'13 inthe time interval t-1 to t1. Rise of current infcoil 13 causes a voltagedrop across it which in turn generates a current :'.1q of Figure llithrough the resistor 47 and the coil 46.

ICombined action of the current :'13 in coil 13 and i.1q in coil `46results in a strong attraction of the movable armature 14 towards thecoil 13 which magnetizes in the same direction as the bias coil 42 and astrong repulsion ofthe movable armature 14 away from the coil 46 whichmagnetizes in the opposite direction of the bias coil 41. Armature 14then starts to move from the open towards the closed-position.

At the time t1 andk saturable transformer core 17 is fully saturated.lCurrent 20 through coils 18 and 20 can rise again, now being suppliedfrom a positive generator voltage e10, whereas the capacitor voltage egqdecays rapidly and reaches zero at t2.

As long as the capacitor 37 was charged, 2a discharge current throughthe circ-nit 37-393634-24--2037 was prevented by the rectifier 34. AtVthe instant t2, when e0q reaches zero, a current starts flowing throughrectier 34 through the circuit 10-1318-243436 28--11-10 since theimpedance of this circuit is lower than that of the by-pass circuitthrough 20--26-'27-35. Positive current through coil 24, however, causescore 25 to unsaturate immediately thereby limiting the current kto avery small value and causing all the voltage of the circuit (thegenerator voltage e10) to appear oncoil 24 as shown by e21 of Figure11d.

This means that the left hand side of the coil 24 assumes the potentialof the right hand side of 10 and thus the voltage on the contact 14collapses as shown by e1.,g in Figure 11b.

`Only remaining passage of the main current :'10 is through10-13-18-20-26-27-35-28-11-10, because current through coil 24 isnegligible. Hence the only voltage appearing on the contacts 14 isvoltage drop across coil 28 due to the current :'20. To compensate forthis voltage drop, a resistor 35 and a choke 27 are inserted into theby-pass circuit, the ratio of which corresponds to theresistance-inductance ratio of the coil 28 but which is larger in amountthan 2S. Transformer 36 has a number of turns ratio equivalent to theratio of magnitudes between 35--27 and 28. Thus the real volt- .ageacross contact 114 is only the difference between the voltage drop oncoil 28 and the drop of resistor 35 :and inductor as transformednegatively by 36. In Figure 1lb this is shown as a small voltage e1.1appearing after t1. Practically however theL voltage will beimperceptibly small.

In the time interval t2--t4, the above mentioned con ditions remainstationary with the by-pass current steadily increasing as shown inFigure llf. The generator voltage appears as shown in Figure 11d as e2.1on coil 24. The currents :'13 through the coil 13 and :',1q through coil46 remaining approximately constant, thereby maintaining a constantforce upon the armature 14, across which the voltage e1,1 isapproximately zero.

A spark suppressor circuit comprising the capacitor 57 and resistor 58is shown in Figure l0 as being connected directly :across theelectromagnetic switch contact 14. Capacitor 57 which was chargednegatively during the time i12 to t1 discharges itself through theresistor 58 because the voltage across the switch 1-4 is Zero.

When the armature 14 has travelled the full closing distance, it closesat the time t3. As it closes there will be not voltage lacross it, andinrush current will not flow. Even if the contact bounces there will beno arc and no recovery voltage. That is to say that the A.C. biascurrent in coil 51 and the D.C. bias in coil 52 can be adjusted tocompensate for the magnetizing current of core 25 to make this residualcurrent negligibly small, assuring not only a voltage-less but also acurrent-less closing of the contact.

At the time t4 the core 25 saturates 4and a low impedance path is nowprovided in the circuit 10-13-18- 24-14-11-10 and the current risesfreely as shown by :'24c in Figure 11d. The by-pass current :'20 nowdecays gradually according to the inductance and resistance of 35 and27.

Voltage across the load e11 appears suddenly at the time t4, becausealmost Iall the impedance of the rectifier has been short-circuited,such that the load voltage en equals the generator voltage e10 as shownin Figure llg.

Break process for complete circuit of Figure 10 At the time t6 thecurrent :'10 in the main line as shown in Figure lla decreases andreaches the unsaturation level of the saturable transformer at the timet7.

Similarly, the unsaturation level of the saturable transformer at themake is the level at the break as given by the D.C. bias of the coil 19.Hence when the ampereturns of coils 18 and 19 become equal, the core 17unsaturates and the impedance of the coil 18 suddenly assumes a veryhigh value. The generator voltage el@ shown as en in Figure 11g whichwas applied to the load is suddenly transferred to the higher impedanceof the coil 18 as shown in Figure 11e` as em. Further reduction of theline current :'10 of Figure 11a proceeds at a lower rate. Voltageappearing on coil 18 is transformed into the coil 20, giving rise to acirculatory current :20 of Figure l1 f which iiows through the circuit20-26-27-35-28-14--24-20. Circulatory current :'20 opposes the maincurrent :24 flowing through the coil 24 and the contact 14, so that :324decreases very rapidly to zero, as seen in Figure 11d.

At the time t8, the current :'24 has reached zero and the current :'20has reached the value of im in the generator as shown in Figures lla,11d and llf. Now the core 25 of the commutating reactor unsaturatescausing the impedance of coil 24 to become almost infinite and thecurrent :'24 therefore remains -at the zero value and the voltage e24across the coil 24 rises sharply, as shown in Figure 11d. The by-passcurrent :'20 on the other hand, is stopped in its rise and is now equalto the main current im as shown in Figures lla and llf.

During the time interval t7t9, the voltage appearing on the saturabletransformer coils 18 and 20, shown as els in Figure llc, is transformedinto coil 48. This voltage is opposed to the voltage appearing duringthe make and generates a current :'48 in the circuit 48-50- 49-13-48,which opposes the main current as seen in Figure 11h. Total currentowing through the drive magnet coil 13, shown as :'13 in Figure 11h, isdecreasing ;harply after the time t7, even turning negative after t8. Atthe same time, decreasing current in coil 13 induces a negative voltageon its terminals (coil 13 is almost a pure inductor), which in turngenerates a negative current :'42 through the coil 46. Current :'13 incoil 13 and current i4? in coil 46 both contribute to demagnetize theclosing pole 40 and magnetize the opening pole 41 of the drive magnet,causing a positive and powerful action upon the armature 14. At the timetlf), the armature has overcome its inertia and opens the circuit.

Current flow through the armature is prevented by the commutatingreactor coil 24 during the time interval t8-t12, as the magnetizingcurrent of core Z5 is supplied by the D.C. bias 52 and the A.C. bias 51.Therefore the residual current through the armature is negligible as(shown by :'24 in Figure 11d).

The small residual current which does flow through armature 14 duringthe actual break at the time t10 however finds a low impedance by-passthrough the spark suppressor circuit 57-58.

Current :'20 through the by-pass circuit finally reaches zero at thetime t11 as shown in Figure llf and reversal of this current isprevented by the semi-conductor rectifier 26.

Extension to three phase systems It is now obvious that the circuitrydescribed heretofore with reference to a single phase half wave unit ora single phase full wave unit can now be easily extended to the case ofthe three-phase half wave unit as shown in Figure l2.

In this figure, which contains all the elements of 10, all like elementshave similar numbers and a cursory inspection of Figure l2 shows that ismerely the application of the single phase half wave circuit of Figure lrepeated three times. This circuit diagram could similarly be extendedto the case of a three-phase full wave rectifier. It is similarly tructhat the basic circuit of Figure l and each of the novel elements shown24 specifically in Figures 4 through 8 could be applied to anyconnection for an electromagnetic rectier.

There is, however, one minor difference between the circuits of Figure10 and Figure l2. In Figure 12, it will be noted that the A.C. biasphase shifter was deleted because advantage has been taken of thethreephase arrangement to supply through the smoothing choke 63 A.C.bias power out of phase with the main voltage. The operation of theparticular three-phase half wave circuit shown in Figure 12 will beobvious to any one skilled in the art and having knowledge of theoperation of a single phase half wave rectifier shown and described withFigure l0.

Although I have described preferred embodiments of my invention, it willnow be obvious that many variations and modifications may be made bythose skilled in the art and I therefore prefer to be limited, not bythe specific disclosure herein, but only by the appended claims.

I claim:

l. In an electromagnetic rectifier for energizing a D.C. load from anA.C. source, `an electromagnetic switchihaving a first and secondcontact and operating means to operate said first and second contactinto and out of engagement in synchronism with the frequency of saidA.C. source, a by-pass circuit, a commutating reactor having a core ofeasily saturable type material and a winding, at least said A.C. source,electromagnetic switch first and second contacts, commutating reactorwinding and D.C. load forming a closed `series connection when saidfirst and second contact are in the engaged position, said by-passcircuit containing a first valve means connected in series with saidA.C. source and a regulating means comprising a regulating core and awinding and in parallel with said first and second contact and havingcircuit connections for energizing said electromagnetic switch operatingmeans for effecting contact closure at a. predetermined time; a makepreexcitation circuit comprising a second valve; said second valve beingconnected in series with said commutating reactor during the makeprocess and being connected in parallel with said first and secondelectromagnetic switch contacts to form a closed series connection ofsaid first and second electromagnetic switch contacts and saidregulating core winding, the voltage appearing on said first and secondcontacts at the make being the forward voltage drop of said secondvalve.

2. In an electromagnetic rectifier for connecting an A.C. source to aD.C. load comprising a pair of contacts being constructed to move intoand out of engagement responsive to the variations of a magnetic field,a commutating reactor having a winding connected in series with saidcontacts and energizing means for creating a magnetic field for movingsaid contacts into and out of engagement responsive to the instantaneousvalue of said A.C. source; a make pre-excitation circuit, said makepre-excitation circuit comprising a diode connected in series with saidcommutating reactor winding and in parallel with said pair of contacts,said diode being connected to conduct magnetizing current of saidcommutating reactor during the make interval.

3. In an electromagnetic rectifier for energizing a D.C. load from anA.C. source, an electromagnetic switch having a first and second contactand operating means to operate said first and second contacts into andout of engagement in synchronism with the frequency of said A.C. source,a by-pass circuit, a commutating reactor having a core of easilysaturable type material and a winding, at least said A.C. source,electromagnetic switch first and second contacts, commutating reactorwinding and D.C. load forming a closed series connection when said firstand second contacts are in the engaged position, said by-pass circuitcontaining a first valve means connected in series with said A.C. sourceand a regulating means comprising a regulating core and a Winding anda-,eoassfi l parallel with said 'first and second contact and having`circuit connections for energizing said electromagnetic switchoperating means for effecting contact closure at a predetermined time; amake pre-excitation circuit comprising a second valve; said second valvebeing connected in 'series with said commutating reactor for carryingmagnetiz'i'ng current of said commutating reactor during the makeprocess and being connected in parallel with said `first andr secondelectromagnetic switch contacts to form `a closed series connection ofsaid first and second electromagnetic switch contacts and saidregulating core Winding, the voltage appearing on said first and secondcontacts at the make being the forward voltage drop of said ksecondvalve, and means comprising a measure of the impedance of said regulatorwinding when said regu- -la'to'r ycore' is saturated for inducing avoltage in said last mentioned closed circuit having an equal magnitudeand `opposite direction to the voltage drop appearing on said regulatorvcore winding.

l4. In an electromagnetic rectifier for energizing a D.'C. load Vfrom anA.C. source, an electromagnetic switch having a first and second contactand operating means to operate said first and second contacts into andyout of engagement in synchronism with the frequency of said A.C.source, a by-pass circuit, a commutating reactor having a core of easilysaturable type material and a winding, at least said A.C. source,electromagnetic switch first and second contacts, commutating reactorwinding and D.C. load forming a closed series connec- 'tion when saidfirst and second contacts are in the engaged position, said by-passcircuit containing a first valve means being connected in series withsaid A.C. source and a regulating means comprising a regulating core anda winding and in parallel with said first and second con- 'tact andhaving circuit connections for energizing said electromagnetic switchoperating means for effecting contact closure at a predetermined time; amake pre-excitation circuit comprising a second valve; said second valvebeing connected in series with said commutating reactor for carryingmagnetizing current of said commutating reactor during the make processand being connected in parallel with said first and secondelectromagnetic switch contacts -to form a closed series connection ofsaid first and second electromagnetic switch contacts and saidregulating core winding, the voltage appearing on said 'first and secondcontacts at the make being the forward voltage drop of said secondvalve, said last mentioned closed series circuit containing a resistorand inductor connected to carry the by-pass circuit current and atransformer positioned to carry the current of said make preexcitationcircuit, the impedance of said resistance and inductance beingproportional to the air impedance of said regulator winding; the voltagedrop on said resistor and inductor being impressed on the primary ofsaid transformer, the secondary winding of said transformer beingconstructed to impress a voltage of equal magnitude and opposite phaseof that appearing on said regulator winding into said last Amentionedclosed circuit.

5. In an electromagnetic rectifier of the type having a makepre-excitation circuit, by-pass circuit, a regulat ing core having awinding and electromagnetically operated contacts wherein byfpasscircuit current flowing through said regulator winding achievesoperation of said contacts, said contacts, make pre-excitation circuit,and regulator winding forming a closed series circuit; a means tocompensate for the voltage drop due to by-pass circuit current throughkthe regulator winding comprising measuring means Vfor measuring thesaid voltage drop and inserting the substantially same voltage asappears on the said regulator winding on the said closed series circuitin a direction to compensate for the voltage drop on the said regulatorwinding to thereby reduce the Voltage appearing across said contacts -toa substantially zero value.

6. yIn an electromagnetic rectifier of the type having a makepre-excitation circuit, by-pass circuit, a regulating core having awinding and electromagnetically operated contacts wherein by-passcircuit current flowing through said regulator winding achievesoperation of said contacts, said contacts, make pre-excitation circuit,Iand regulator winding forming a closed series circuit; a means tocompensate for the voltage drop due to by-pass circuit current throughthe regulator winding; said means comprising an impedance which isproportional to the air impedance of said regulator winding beingconnected in series with said by-pass circuit winding, the voltage dropon said measuring impedance being applied to the primary winding of atransformer and inserting the .substantially same voltage as appeared onthe said regulator winding in a direction to compensate for the voltagedrop on the said regulator winding by means of the secondary winding ofsaid transformer thereby reducing the voltage appearing across saidcontacts to a substantially zero value.

7. In an electromagnetic rectifier for energizing a D.C. load from anA.C. source comprising an electromagnetic switch having contactslmovable into and out of engagement responsive to a magnetic field andmeans for creating said magnetic `field in synchronism with thefrequency of said A.C. source, a commutating reactor having a core ofsaturaible type material and a winding and a by-pass circuit; saidby-pass circuit containing a diode and having circuit connections forenergizing said means for creating the said magnetic field for movingsaid contacts into the said engaged position, said by-pass circuitconducting current after the potential of said A.C. source is in thedirection `desired for energization of said D.C. load; a pre-energizingmeans for passing current through said by-pass circuit prior to the timeat which by-pass circuit current can -be initiated by said A.C. source;said pre-energizing means comprising a capacitor connected in parallelto said by-pass circuit diode.

8. In an electromagnetic rectifier for energizing a D.C. load from .anA.C. source comprising an electromagnetic switch having contacts movableinto and out of engagement responsive to a magnetic field and means forcreating said magnetic field in sy'nchronism with the frequency of saidA.C. source, a commutating reactor having a core of saturable typematerial and a winding and a by-pass circuit; said bypass circuitcontaining a diode and having circuit connections for energizing saidImeans Ifor creating the said magnetic field for moving said contactsinto the said engaged position, said by-pass circuit conducting currentkafter the potential of said A.C, source is in the direction desired forenergization of said D.-C. load; a pre-energizing means for passingcurrent through said lay-pass circuit prior to the time at which by-passcircuit current can be initiated by said A.C. source; saidpre-energizing means comprising a capacitor connected in parallel tosaid by-pass circuit diode, said capacitor being charged by theinversevolt- -age of said A.C. source appearing across said `by-passcircuit diode, the voltage of said capacitor exceeding the inversevoltage of said A.C. source at a predetermined time to thereby initiateby-pass circuit current before said A.C. source inverse voltage becomeszero.

9. In an electromagnetic rectifier for energizing a D.C. load from anA,C. source comprising an electromagnetic switch having contacts movableinto and out of engagement responsive to a magnetic field and means forcreating said magnetic field in synchronism with the frequency of saidA.C. source, a commutating reactor having a core of saturable typematerial and a winding and a by-pass circuit; said by-pass circuitcontaining a diode and having circuit connections for energizing saidmeans for creating the said magnetic field for moving said contacts intothe said engaged position, said yby-pass circuit conducting currentafter the potential of said A.C. source is in the direction desired for.energization of said D.C. load; a pre-energizing means for passing

